This invention relates to a photographic material having an improved antistatic property, and more particularly, to a photographic material having an antistatic property that is retained over an extended period of time.
Photographic light-sensitive materials generally comprise an electrically insulative support and one or more photographic layers. Therefore, electrostatic charges often accumulate during the production of photographic light-sensitive materials or upon use thereof due to contact friction with, or delamination from, the surfaces of the same or different materials. This accumulation of electrostatic charge may result in several problems, the most serious of which is the formation of spots, or tree-like or fur-like lines upon development of exposed photographic films, due to the discharge of the accumulated electrostatic charge before development (since the discharge excites the light-sensitive layer). This is the so-called static marks, which seriously affects commercial value of photographic films and, in extreme cases, can completely destroy the commercial value. For example, it can readily be understood that such static marks on X-ray films for medical or industrial use could lead to an extremely dangerous misdiagnosis. This phenomenon is an extremely difficult problem, because it is only observed after development. In addition, the accumulated electrostatic charge can cause secondary problems, such as adhesion of dust to the film surface and non-uniform coating.
As is explained above, such electrostatic charges often accumulate upon production and use of photographic light-sensitive materials. In the production steps, the electrostatic charge develops due to contact friction between photographic films and rollers or separation of the support surface from the emulsion surface during the film-winding or film-unwinding. With finished products, it develops due to separation of a base surface and an emulsion surface from each other upon winding up and charging films, or contact or separation of X-ray films with or from mechanical members or fluorescent brightening paper in an automatic photographing machine.
Static marks in photographic light-sensitive materials formed by the accumulated electrostatic charge become a more serious problem as the sensitivity of the photographic light-sensitive materials increases and as the processing speed increases. Particularly, photographic light-sensitive materials have in more recent times often been subjected to severe processing conditions, e.g., to increase sensitivity high-speed coating, high-speed photographing, high-speed automatic processing, etc., and hence static marks have occurred more readily.
The best solution to the problem of static electricity is to increase the conductivity of the photographic materials, thus allowing the charge to dissipate in a short time prior to discharge of the accumulated charge.
Thus, attempts have been made to improve the conductivity of the support and various surface-coating layers of photographic light-sensitive materials using various hygroscopic materials, water-soluble inorganic salts, certain kinds of surfactants, polymers, etc. Thus, the polymers described, for example, in U.S. Pat. Nos. 2,882,157, 2,972,535, 3,062,785, 3,262,807, 3,514,291, 3,615,157, 3,753,716, 3,938,999, etc., the surfactants described, for example, in U.S. Pat. Nos. 2,982,651, 3,428,456, 3,457,076, 3,454,625, 3,552,972, 3,655,387, etc., and zinc oxide, semiconductors, colloidal silica, etc., described, for example, in U.S. Pat. Nos. 3,062,700, 3,245,833, and 3,525,621 have been used.
However, the property of these materials are rather specific, and depend so much upon the kind of the film support and the photographic composition, that while they provide good results with some particular film supports and photographic constituents (e.g., photographic emulsions), they are completely useless for preventing development of static electricity with other film supports and photographic constituents and, in some cases, exert a detrimental influence on the photographic properties. In particular, it has been extremely difficult to prevent development of electrostatic charge on a hydrophilic colloidal layer and, in many cases, there results an insufficient reduction in surface resistance under conditions of low humidity or adhesion between the photographic light-sensitive materials or between a photographic light-sensitive material and other material under a high temperature and high humidity conditions.
On the other hand, some materials cannot be used due to their detrimental influences on photographic properties such as sensitivity of the photographic emulsion, fog, graininess, sharpness, etc., in spite of their excellent antistatic effect. An example is polyethylene oxide series compounds, generally known to have an antistatic effect. For instance, polyethylene oxide series compounds, generally known to have an antistatic effect, often exert detrimental influences on photographic properties such as an increase of fog, desensitization, deterioration of graininess, etc. In particular, it has been difficult to effectively impart an antistatic property to light-sensitive materials having photographic emulsions on both sides of a support, such as X-ray sensitive materials for medical use, without detrimentally influencing the photographic properties.
Furthermore, most of the conventional antistatic photographic materials become less antistatic as time goes by, and it has been particularly difficult to establish a technique that provides a photographic material which retains the antistatic property over an extended period of time. Even compounds that are effective as an antistat interfere with the application of a photographic layer that contains the antistat. Because of this, in most cases, the provision of an antistatic property in a photographic material is extremely difficult to achieve, and a photographic material including an antistatic agent (antistat) may have limited utility.